Surface-emitting type light-emitting diode and fabrication method thereof

ABSTRACT

Disclosed is a surface-emitting type light-emitting diode including a substrate, a p-n junction layer elevated on a portion of the substrate to emit light, and a first isolator layer formed on a sidewall of the p-n junction layer as well as a periphery portion of a top surface of the p-n junction layer except for a central region of the top surface.

This application is a Divisional of co-pending application Ser. No.10/636,591 filed on Aug. 8, 2003, and for which priority is claimedunder 35 U.S.C. § 120; and this application claims priority ofApplication No. 47158/2002 and 47159/2002 filed in Korea on Aug. 9, 2002under 35 U.S.C. § 119; the entire contents of all are herebyincorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a surface-emitting type light-emittingdiode, and more particularly, to a surface-emitting type light-emittingdiode that can accurately measure a distance by emitting light only froma desire surface thereof. The present invention is further directed to amethod for fabricating such a surface-emitting type light-emittingdiode.

2. Description of the Related Art

Generally, a light-emitting diode (LED) is a device converting anelectric energy into a light energy with a high efficiency to therebyobtain a high output at a low current. In addition, the LED has a highresponse speed, and enables the high-frequency modulation. Furthermore,the LED is designed such that the light output thereof can be readilyvaried by a current control and it is controlled by either a direct oralternating current.

Such an LED can be employed to a variety of applications such as asensor device and a distance-measuring device as it can be designed tobe small-sized and lightweight with a long lasting and low powerconsumption. Particularly, the LED has been used as a device formeasuring a distance in an iris scan system.

As is well known, the iris scan system is a security system to certify apersonal identification to allow only the certified person to enter intoa limited area or to access limited information. The iris scan systemhas a high recognition rate and accuracy compared with a fingerprintscan system.

The iris scan system takes a photograph of an iris, makes image data byimage-processing a typical pattern of the photographed image, andcompares the image data with a pre-registered iris data, therebycertifying a personal identification.

In such an iris scan system, a position sensitive detector (PSD) formeasuring a distance to a user has been used. The PSD has a lightemission part and a light reception part. When light is emitted from thelight emission part, the light reception part receives the lightreflected from an object to measure the distance between the object andthe PSD using a triangular surveying. However, the PSD is too expensiveto be employed to the iris scan system that should be widely used withmoderate prices. In addition, the PSD occurs frequent errors inmeasuring the distance.

Accordingly, a low-priced iris scan system using the LED has beendeveloped to measure the distance by catching a location of the LEDappearing on a photographed image. That is, by installing apre-calculated algorithm in the iris scan system, the distance to theobject can be accurately and quickly measured by detecting the locationof the LED appearing on the photographed image.

However, such a conventional surface-emitting type LED has a problemthat can be described in conjunction with FIG. 1 showing a side-emittingproblem of the conventional surface-emitting type LED.

That is, as shown in FIG. 1, even with a masking process, theconventional surface-emitting type LED 100 is designed to emit lightfrom a peripheral light-emitting region 120 as well as a desiredemitting region 110. Therefore, in the iris scan system employing such aconventional surface-emitting type LED, the accuracy of the measurementof the object distance is deteriorated due to the light emission at theperipheral light-emitting region 120.

SUMMARY OF THE INVENTION

Accordingly, the present invention is directed to a surface-emittingtype LED and a method for fabricating the same that substantiallyobviate one or more problems due to limitations and disadvantages of therelated art.

An object of the present invention is to provide a surface-emitting typeLED and a method for fabricating the same that accurately measure adistance by preventing the light emission at a peripheral surface regionthereof.

Additional advantages, objects, and features of the invention will beset forth in part in the description which follows and in part willbecome apparent to those having ordinary skill in the art uponexamination of the following or may be learned from practice of theinvention. The objectives and other advantages of the invention may berealized and attained by the structure particularly pointed out in thewritten description and claims hereof as well as the appended drawings.

To achieve these objects and other advantages and in accordance with thepurpose of the invention, as embodied and broadly described herein,there is provided a surface-emitting type light-emitting diodecomprising a substrate; a p-n junction layer elevated on a portion ofthe substrate to emit light; and an isolator layer formed on a sidewallof the p-n junction layer as well as a periphery portion of a topsurface of the p-n junction layer except for a central region of the topsurface.

In another aspect of the present invention, there is provided asurface-emitting type light-emitting diode comprising a substrate; a p-njunction layer to emit light having an n-type epitaxial layer elevatedon a portion of the substrate and a p-type epitaxial layer formed on acentral region of a top surface of the n-type epitaxial layer; and anisolator layer formed on a sidewall of the p-n junction layer as well asa periphery portion of a top surface of the p-n junction layer exceptfor a central region of the top surface.

In still another aspect of the present invention, there is provided amethod for fabricating a surface-emitting type light-emitting diode. Themethod comprises the steps of depositing a p-n junction layer on asubstrate; etching the p-n junction layer and the substrate to dividedthe p-n junction layer into a plurality of blocks elevated on thesubstrate in a matrix-shape; forming an isolator layer on a sidewall ofthe p-n junction layer as well as a periphery portion of a top surfaceof the p-n junction layer except for a central region of the topsurface; and cutting the blocks to provide a plurality of light-emittingdiodes.

In still yet another aspect of the present invention, there is provideda method for fabricating a surface-emitting type light-emitting diode.The method comprises the steps of depositing an n-type epitaxial layeron a substrate; etching the n-type epitaxial layer and the substrate todivide the n-type epitaxial layer into a plurality of blocks elevated onthe substrate in a matrix-shape; forming an isolator layer on a sidewallof the n-type epitaxial layer as well as a periphery portion of a topsurface of the n-type epitaxial layer except for a central region of thetop surface; forming a p-n junction by forming a p-type epitaxial layeron a top surface of the n-type epitaxial layer by doping p-type ions;and cutting the blocks to provide a plurality of light-emitting diodes.

It is to be understood that both the foregoing general description andthe following detailed description of the present invention areexemplary and explanatory and are intended to provide furtherexplanation of the invention as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention and are incorporated in and constitute apart of this application, illustrate embodiment(s) of the invention andtogether with the description serve to explain the principle of theinvention. In the drawings:

FIG. 1 is a schematic view of a conventional surface-emitting type LEDillustrating a peripheral light-emitting phenomenon;

FIGS. 2A to 2C are views illustrating a method for fabricating asurface-emitting type LED according to a first embodiment of the presentinvention;

FIGS. 3A to 3D are views illustrating a method for fabricating asurface-emitting type LED according to a second embodiment of thepresent invention;

FIGS. 4A to 4D are views illustrating a method for fabricating asurface-emitting type LED according to a third embodiment of the presentinvention; and

FIG. 5 is a sectional view of a surface-emitting type LED according to afourth embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Reference will now be made in detail to the preferred embodiments of thepresent invention, examples of which are illustrated in the accompanyingdrawings.

FIRST EMBODIMENT

FIGS. 2A to 2C show a method for fabricating a surface-emitting type LEDaccording to a first embodiment of the present invention.

Referring first to FIG. 2A, an epitaxial layer 202 is first deposited ona substrate 201, thereby forming a wafer.

Here, the epitaxial layer 202 deposited on the substrate 201 is a p-njunction layer formed by layering an n-type clad layer, an active layer,and a p-type clad layer in this order. Although it is not shown in thedrawing, a buffer layer may be further formed between the substrate 201and the epitaxial layer 202.

Afterwards, the wafer deposited with the epitaxial layer 202 is cleaned,and the epitaxial layer 202 and the substrate 201 are etched in apredetermined patterned as shown in FIG. 2B.

Describing in more detail, before the pattern is formed, a photoresistlayer is deposited on the wafer at a predetermined thickness through,for example, a spin coating process.

After the above, a mask having a desire pattern is disposed on thephotoresist layer, and a light exposure process is performed byilluminating ultraviolet rays. Then, a developing process is performedusing a developing solution, thereby developing the pattern by use of asolubility difference between the light-exposing portion and thenon-exposing portion, after which an etching process is performed toobtain the pattern as shown in FIG. 2B. That is, the epitaxial layer 202and the substrate 201 are etched such that the epitaxial layer 202 canbe divided into a plurality of blocks in a matrix-shape on the substrate201.

Afterwards, as shown in FIG. 2C, an isolator layer 203 is formed on eachblock of the epitaxial layer 202 by use of a lift-off process.

Describing the lift-off process in brief, a photoresist layer is formedin a desire pattern and a thin film layer is formed on the photoresistlayer. Then, a portion of the thin film layer, which is formed on thephotoresist layer, is removed together the photoresist layer such thatonly a portion of the thin film layer, which is not formed on thephotoresist layer, is remained, thereby forming a desire pattern of thethin film layer. Since such a lift-off process is well known in the art,the detailed description thereof will be omitted herein.

Further describing the process for forming the LED as shown in FIG. 2C,a photoresist layer (not shown) is first patterned on a desire centrallight-emitting region of the blocks of the epitaxial layer 202 elevatedon the substrate 201, and the isolating layer 203 is then depositedcovering the substrate 201, the photoresist layer, and the epitaxiallayer 202.

Here, the isolating layer 203 is formed of oxide such as SiO₂ and Al₂O₃or polymer, and is deposited at a thickness of about 1-30 μm through asputtering process. At this point, the isolator layer 203 is formed of aplurality of oxide layers, having a predetermined thickness inaccordance with a refraction index of the oxide used. That is, thethickness is set to be about λ/4n (where, the λ indicates wavelength oflight emitted from the LED, and the n indicates the refraction index ofthe material of the isolator layer).

Afterwards, a portion of the isolator layer 203 formed on thephotoresist layer is removed together with the photoresist layer,thereby obtaining a desire pattern of the isolator layer 203 as shown inFIG. 2C.

The wafer having the plurality of blocks in the matrix-shape is then cutto obtain a plurality of LEDs.

The LED fabricated as in the above is designed to emit light only at theexposed region of the epitaxial layer 202. Therefore, when the iris scansystem employs such an LED, the object distance can be more accuratelymeasured.

SECOND EMBODIMENT

FIGS. 3A to 3D show a method for fabricating a surface-emitting type LEDaccording to a second embodiment of the present invention.

Referring first to FIG. 3A, an epitaxial layer 302 is first deposited ona substrate 301, thereby forming a wafer.

Here, the epitaxial layer 302 deposited on the substrate 301 is a p-njunction layer formed by layering an n-type clad layer, an active layer,and a p-type clad layer in this order. Although it is not shown in thedrawing, a buffer layer may be further formed between the substrate 301and the epitaxial layer 302.

Afterwards, the wafer deposited with the epitaxial layer 302 is cleaned,and the epitaxial layer 302 and the substrate 301 are etched in apredetermined patterned as shown in FIG. 3B. That is, the epitaxiallayer 302 and the substrate 301 are etched such that the epitaxial layer302 can be divided into a plurality of blocks in a matrix-shape on thesubstrate 301.

Afterwards, as shown in FIG. 3C, an isolator layer 303 is formed on eachblock of the epitaxial layer 302 by use of a lift-off process.

Further describing the process for forming the LED as shown in FIG. 3C,a photoresist layer (not shown) is first formed on a portion slightlylarger than a desire central light-emitting region of the blocks of theepitaxial layer 302 elevated on the substrate 301, and the isolatinglayer 303 is then deposited covering the substrate 301, the photoresistlayer, and the epitaxial layer 302.

Here, the isolating layer 303 is formed of oxide such as SiO₂ and Al₂O₃or polymer, and is deposited at a thickness of about 1-30 μm using asputtering process. At this point, the isolator layer 303 is formed of aplurality of oxide layers, having a predetermined thickness inaccordance with a refraction index of the oxide used. That is, thethickness is set to be about λ/4n (where, the λ indicates wavelength oflight emitted from the LED, and the n indicates the refraction index ofthe material of the isolator layer).

Afterwards, a portion of the isolator layer 303 formed on thephotoresist layer is removed together with the photoresist layer,thereby obtaining a desire pattern of the isolator layer 303 as shown inFIG. 3C.

Next, as shown in FIG. 3D, a metal layer 304 is formed through thelift-off process.

That is, a photoresist layer (not shown) is formed on a desire centrallight-emitting region of the epitaxial layer 302 elevated on thesubstrate 301, after which the metal layer 304 is deposited covering theisolator layer 303, the epitaxial layer 302, and the photoresist layer.

Here, the metal layer 304 is formed of a material selected from thegroup consisting of Au, Ti, Al and Ag, or a combination thereof suchTi/Pt/Au. The metal layer has an identical property to a lead lineenhancing the contacting force. At this point, the metal layer has apredetermined thickness, preferably, of about 1-30 μm.

Afterwards, a portion of the metal layer 304, which is formed on thephotoresist layer, is removed together with the photoresist layer,thereby obtaining a pattern as shown in FIG. 3D.

After the above, the substrate 301 is cut into a plurality of the blockshaving the matrix-shape, thereby fabricating a plurality of LEDs.

Accordingly, the LEDs having the above-described structure are designedto emit light only at the exposed region of the epitaxial layer 302.Therefore, when the iris scan system employs such an LED, the objectdistance can be more accurately measured.

THIRD EMBODIMENT

FIGS. 4A to 4D show a method for fabricating a surface-emitting type LEDaccording to a third embodiment of the present invention.

Referring first to FIG. 4A, an n-type epitaxial layer 402 is firstdeposited on a substrate 401, thereby forming a wafer.

Afterwards, the wafer deposited with the n-type epitaxial layer 402 iscleaned, and the n-type epitaxial layer 302 and the substrate 301 areetched in a predetermined patterned as shown in FIG. 4B. That is, then-type epitaxial layer 402 and the substrate 401 are etched such thatthe n-type epitaxial layer 402 can be divided into a plurality of blocksin a matrix-shape on the substrate 401.

Afterwards, as shown in FIG. 4C, an isolator layer 403 is formed on eachblock of the epitaxial layer 402 through a lift-off process.

Further describing the process for forming the LED as shown in FIG. 4C,a photoresist layer (not shown) is first formed on a desire centrallight-emitting region of the blocks of the epitaxial layer 402 elevatedon the substrate 401, and the isolating layer 403 is then depositedcovering the substrate 401, the photoresist layer, and the epitaxiallayer 402.

Here, the isolating layer 303 is formed of oxide such as SiO₂ and Al₂O₃or polymer, and is deposited at a thickness of about 1-30 μm using asputtering process. At this point, the isolator layer 403 is formed of aplurality of oxide layers, having a predetermined thickness inaccordance with a refraction index of the oxide used. That is, thethickness is set to be about λ/4n (where, the λ indicates wavelength oflight emitted from the LED, and the n indicates the refraction index ofthe material of the isolator layer).

Afterwards, a portion of the isolator layer 403 formed on thephotoresist layer is removed together with the photoresist layer,thereby obtaining a desire pattern of the isolator layer 303 as shown inFIG. 4C.

Next, as shown in FIG. 4D, p-type ions are doped in the n-type epitaxiallayer 402 through an ion implantation process. At this point, theisolator layer 403 functions as a mask for doping the ions in theepitaxial layer 402. As a result, the p-type ions are doped in only aportion of the epitaxial layer 404, which is not covered with theisolator layer 403, thereby varying a predetermined upper portion of then-type epitaxial layer 402 into a p-type epitaxial layer 404. At thispoint, the p-type epitaxial layer 404 has a thickness of about 10-30 μm.

The LED structured as in the above is designed to emit light only at ap-n junction of the n-type epitaxial layer 402 and the p-type epitaxiallayer 404.

After the above, the substrate 401 is cut into a plurality of the blockshaving the matrix-shape, thereby fabricating a plurality of LEDs.

Therefore, when the iris scan system employs such an LED, the objectdistance can be more accurately measured.

Meanwhile, the doped ions can be one of the n-type and p-type ions inaccordance with the property of the wafer. That is, when the wafer isthe p-type, the n-type ions are doped, and when it is the n-type, thep-type ions are doped.

Furthermore, when a p-n junction of the n-type epitaxial layer 402 andthe p-type epitaxial layer 404 is formed through the ion implantationprocess, the light-emitting region can be formed in a specific shape bymodifying the mask for blocking the ions. For example, when the shape ofthe mask is designed in a stick-shape or a heart-shape, the p-typeepitaxial layer 404 formed by doping the p-type ions can be formed inthe stick-shape or in the heart-shape. As a result, an LED that isdesigned to emit light having the stick-shape or the heart-shape can berealized.

FOURTH EMBODIMENT

As is well known, an electrode should be formed to drive asurface-emitting type LED. In the present invention, the electrode isnot formed on an entire top surface of the epitaxial layer 502, but on alimited desire portion of the top surface. Here, the limited desireportion indicates a desire light-emitting region.

In addition, the epitaxial layer 502 deposited on a substrate 501 is ap-n junction layer formed by layering an n-type clad layer, an activelayer, and a p-type clad layer in this order. Although it is not shownin the drawing, a buffer layer may be further formed between thesubstrate 501 and the epitaxial layer 502.

Describing in more detail, an ohmic metal layer 506 is deposited on apredetermined portion of a top surface of the epitaxial layer 502, and abonding metal layer 507 is formed on the ohmic metal layer 506. That is,the ohmic metal layer 506 is not formed on the entire top surface of theepitaxial layer 502, but formed in a predetermined desire shape on thetop surface of the epitaxial layer 502. Therefore, the ohmic metal layerappears in a plurality of blocks with a space from each other when it isviewed in a section as shown in FIG. 5.

When the ohmic metal layer is formed on the limited desire region, thecurrent flows only at a region where the ohmic metal layer 506 and thebonding metal layer 507 are formed. That is, the current can becontrolled such that it can flow only at a desire region, thereby makingit possible to allow the light to be emitted only at the desire region.

In addition, to prevent the light from being leaked in a side direction,a light-shielding layer 508 formed in a multiple layer is formed on asidewall and a peripheral portion of a top surface of the epitaxiallayer 502.

That is, as shown in FIG. 5, the light-shielding layer 508 is comprisedof a first isolator layer 503, a reflection layer 504, and a secondisolator layer 505. The first and second isolator layers 503 and 505 areformed of an insulating material such as SiO₂, and the reflection layer504 is formed of a metal material such as TiO₂.

Here, being formed of the metal material such as the TiO2, thereflection layer 504 enhances the bonding force between the first andsecond isolator layers 503 and 505 and the light-shielding layer 508 isformed to be thicker, thereby effectively preventing the light emittedfrom the epitaxial layer 502 from being leaked in a side direction.

It will be apparent to those skilled in the art that variousmodifications and variations can be made in the present invention. Thus,it is intended that the present invention covers the modifications andvariations of this invention provided they come within the scope of theappended claims and their equivalents.

1. A method for fabricating a surface-emitting type light-emittingdiode, the method comprising the steps of: depositing a p-n junctionlayer on a substrate; etching the p-n junction layer and the substrateto divide the p-n junction layer into a plurality of blocks elevated onthe substrate in a matrix-shape; forming an isolator layer on a sidewallof the p-n junction layer as well as a periphery portion of a topsurface of the p-n junction layer except for a central region of the topsurface; and cutting the blocks to provide a plurality of light-emittingdiodes.
 2. The method of claim 1, wherein the p-n junction layer isformed by layering a p-type clad layer, an active layer, and an n-typeclad layer.
 3. The method of claim 1, wherein the isolator layer isformed of oxide or polymer.
 4. The method of claim 1, wherein theisolator layer is deposited having a thickness of about λ/4n (where, theλ indicates wavelength of light emitted from the LED, and the nindicates the refraction index of a material of the isolator layer). 5.The method of claim 1, wherein the isolator layer is formed through alift-off process.
 6. The method of claim 1, further comprising the stepof forming a metal layer on the isolator layer.
 7. The method of claim6, wherein the metal layer is formed of a material or a combinationselected from the group consisting of Au, Ti, Al, Ag and Pt.
 8. A methodfor fabricating a surface-emitting type light-emitting diode, the methodcomprising the steps of: depositing an n-type epitaxial layer on asubstrate; etching the n-type epitaxial layer and the substrate todivide the n-type epitaxial layer into a plurality of blocks elevated onthe substrate in a matrix-shape; forming an isolator layer on a sidewallof the n-type epitaxial layer as well as a periphery portion of a topsurface of the n-type epitaxial layer except for a central region of thetop surface; forming a p-n junction by forming a p-type epitaxial layeron a top surface of the n-type epitaxial layer by doping p-type ions;and cutting the blocks to provide a plurality of light-emitting diodes.9. The method of claim 8, wherein the isolator layer is formed of oxideor polymer.
 10. The method of claim 9, wherein the isolator layer isdeposited having a thickness of about λ/4n (where, the λ indicateswavelength of light emitted from the LED, and the n indicates therefraction index of a material of the isolator layer).
 11. The method ofclaim 9, wherein the isolator layer is formed through a lift-offprocess.
 12. The method of claim 9, wherein the p-type ions are dopedthrough an ion implantation process.
 13. The method of claim 12, whereinwhen the p-type ions are doped through the ion implantation process, theisolator layer is used as a mask for blocking the ions.
 14. The methodof claim 12, wherein when the p-type ions are doped through the ionimplantation process, the p-type epitaxial layer is formed in a specificshape by forming a mask in the specific shape when the p-type ions aredoped through the ion implantation process.